Active Implantable medical devices generally comprise a housing, designated a “generator”, that is electrically and mechanically connected to one or more “leads” provided with electrodes intended to come into contact with the patient's tissues where it is desired to apply stimulation pulses and/or to collect an electrical signal: e.g., the myocardium, nerve, and/or muscle tissue.
There are standardized connection systems to ensure the interchangeability of leads and generators that are produced by different manufacturers. Thus, the standards called “IS-1” and “IS-4” define a number of dimensional and electrical characteristics related to leads used for cardiac pacing and cardiac resynchronization therapy (“CRT”). For defibrillation leads, wherein the electrical stresses are more severe given the higher energy pulses to be conducted from the generator to the lead, the standards known as “DF-1” and “DF-4” apply and define the dimensional and electrical characteristics for that system connection.
The complexity of these leads, which already incorporate the specific constraints in terms of electrical energy associated with the particular use, pacing or shock, is increased with the development of multisite devices and intracardiac sensors, such as endocardial acceleration sensors (EA). As a result, in terms of connectivity, there is a growing number of connection plugs, and moreover different standards depending on the plugs.
The benefit brought by a single plug, subject to a single standard, with a plurality of electrical contacts to ensure simultaneously connections to various terminals of the generator for all energy levels, whether for the collection of depolarization signals, for the application of stimulation pulses or for the delivery of defibrillation shock energy, can be understood.
In this context, it is known to have a single “isodiameter” plug connection, that is to say, with a uniform cylindrical shape, for insertion in a counterpart cylindrical cavity of the connector head of the generator. EP 1641084 A1 and its counterpart U.S. Pat. No. 7,175,478 B1 (both assigned to Sorin CRM S.A.S., previously known as ELA Medical) describes such an isodiameter connection plug, with the outer cylindrical surface having a stack of annular electrical contact areas, made of conductive cylindrical rings, and insulating cylindrical zones providing electrical insulation between the conductive rings. To receive such a multipolar connection plug and to connect it to the electrical generator, the connector head of the generator must have a cavity formed similarly (complementary) to the plug itself, in that it also includes a stack of annular electrical contact elements to make electrical contact with the corresponding conductive rings of the connection plug. In this stack, the annular electrical contact elements are alternately separated by annular isolation elements, provided on their inner diameter of sealing rings having a given profile, for application of a radial compression on the insulating cylindrical zones of the connection plug.
Note that, unlike the older embodiments wherein the isolation elements are carried by the lead, they are now arranged in the cavity, which has the advantage of providing new isolation elements each time the generator is replaced.
The term “isolation” used herein applies to both (i) the sealing of the cavity relative to the external environment, vis-à-vis in particular body fluids, and (ii) the electrical insulation, that is to say the low-voltage insulation of the electrical contact areas and elements, as well as the high-voltage insulation of the cavity with the outside environment.
U.S. Pat. Publication No. 2008/0234778 A1 describes a process for producing a connector head, with a silicone resilient monobloc part, extending all along the cavity. This silicone part is molded around a central pin of appropriate shape. To withdraw the pin after reticulation of the silicone, the part is dipped into a bath of n-heptane, which has the effect of swelling the silicone and radially expands the part, then allowing the withdrawal of the molding pin. This expanded state is also used to insert by the central cavity thus released the electrical contact elements, in housings provided in the silicone part. After evaporation of n-heptane, the silicone part resumes its original definitive dimensions, with the electrical contact elements embedded in it. But, because of the flexibility of the elastomer material, it is capable of compression and relaxation and this known method does not guarantee either the coaxiality of electrical contact elements with the isolation elements, or their axial positioning.
Similarly, EP 2228096 A2 and U.S. Pat. Publication No. 2009/0017700 A1 propose a method for producing an elastomer or epoxy connector head, the cavity of which includes elastomer seals. The electrical contacts are interposed between the seals of the cavity through side windows formed in the connector head, which does not control the coaxiality of the electrical contacts with the elastomer seals or their axial positioning. Moreover, the problem of isolation—sealing and electrical insulation—at the interface of elastomer seals and the head is not resolved.
U.S. Pat. No. 7,630,768 B1 and U.S. Pat. Publication No. 2009/0118778 A1 disclose methods for producing a molded connector head in a hard resin (typically polyurethane), to position and assembly, in a very precise and reliable method, electrical contact elements. However, they do not address in any way the implementation of flexible sealing elements, nor the isolation problems of isolating electrical contact elements from each other and from their environment, and sealing of the cavity, in particular from the body fluids.